Compressive creep behaviour of Yb 4 Si 2 O 7 N 2 containing silicon nitride ceramic between 1400 and 1500°C

A Yb₂O₃-SiO₂ doped silicon nitride ceramic, prepared such that the composition was placed directly on the Yb₄Si₂O₇N₂-Si₃N₄ tie line, was hot pressed sintered. The compressive creep behaviour of the sintered Yb₄Si₂O₇N₂-Si₃N₄ material was examined at 1400, 1450 and 1500°C under a stress range of 250-400 MPa in a nitorgen atmosphere. The sintered material exhibited high resistance to creep. The stress exponents were found to be ∼1.9 at 1400°C, ∼2.1 at 1450°C and ∼2.1 at 1500°C. The activation energy obtained was 510 ± 25 kJ mol^-1. The values of the stress exponents and the activation energy suggest a cavitational process, accommodated by grain boundary sliding, viscous flow and solution-reprecipitation, as the most probable dominant creep mechanism.